The answer is that the configuration is missing the `neighbor 10.0.0.1 send-community extended` command under the VPNv4 address-family. For MPLS L3VPN, the `send-community extended` requirement is critical because VPNv4 routes carry route-target extended communities that control route import and export between VRFs; without this command, the PE router will advertise VPNv4 prefixes to its iBGP peer but strip the extended communities, rendering the routes unusable for VRF population. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding that activating a VPNv4 neighbor alone is insufficient—you must explicitly enable extended community propagation, a common trap where candidates assume `activate` implies community support. Remember the memory tip: "Activate the neighbor, then send the community—VPNv4 routes need their tags to travel."
300-410 MPLS L3VPN Practice Question
This 300-410 practice question tests your understanding of mpls l3vpn. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
The neighbor is missing the 'send-community extended' command under the VPNv4 address-family.
Without 'send-community extended', the extended community (RT) is not sent, so the VPNv4 routes will not carry the route-target, and the remote PE will not import them into the correct VRF.
B
The neighbor must be configured under the IPv4 unicast address-family first.
Why wrong: For VPNv4, you only need to activate the neighbor under the VPNv4 address-family. IPv4 unicast activation is optional.
C
The update-source should be the interface facing the peer, not Loopback0.
Why wrong: Using Loopback0 for iBGP is a best practice for stability.
D
The neighbor remote-as should be different for VPNv4 sessions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The neighbor is missing the 'send-community extended' command under the VPNv4 address-family.
The neighbor 10.0.0.1 is an iBGP peer. For VPNv4 address-family, the neighbor must be activated and the extended community must be sent. However, the configuration is missing the 'neighbor 10.0.0.1 send-community extended' command under the VPNv4 address-family? Actually it is present. But there is a subtle issue: the 'neighbor 10.0.0.1 activate' is there. The configuration looks correct. Wait, the question says 'What is wrong?' Possibly the missing 'neighbor 10.0.0.1 send-community extended'? But it's there. Let me check: The command is 'neighbor 10.0.0.1 send-community extended' - that is correct. Actually, the configuration is correct. But perhaps the issue is that the neighbor is not configured under the IPv4 unicast address-family? That is not required for VPNv4. Hmm. Let me think: The configuration is missing the 'neighbor 10.0.0.1 activate' under the IPv4 unicast address-family? But that is not needed. Actually, the configuration is correct. I need to create a misconfiguration. Let me adjust: The configuration shows 'neighbor 10.0.0.1 send-community extended' but the correct command is 'neighbor 10.0.0.1 send-community extended' - that is fine. Maybe the issue is that the 'neighbor 10.0.0.1 activate' is under the VPNv4 address-family, but the 'send-community' command is missing? No, it's there. Perhaps the problem is that the neighbor is not configured with a route-reflector-client? Not necessarily. I'll change the configuration to have a missing 'send-community extended' to make it wrong.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
The neighbor is missing the 'send-community extended' command under the VPNv4 address-family.
Why this is correct
Without 'send-community extended', the extended community (RT) is not sent, so the VPNv4 routes will not carry the route-target, and the remote PE will not import them into the correct VRF.
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
MPLS L3VPN — This question tests MPLS L3VPN — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The neighbor is missing the 'send-community extended' command under the VPNv4 address-family. — The neighbor 10.0.0.1 is an iBGP peer. For VPNv4 address-family, the neighbor must be activated and the extended community must be sent. However, the configuration is missing the 'neighbor 10.0.0.1 send-community extended' command under the VPNv4 address-family? Actually it is present. But there is a subtle issue: the 'neighbor 10.0.0.1 activate' is there. The configuration looks correct. Wait, the question says 'What is wrong?' Possibly the missing 'neighbor 10.0.0.1 send-community extended'? But it's there. Let me check: The command is 'neighbor 10.0.0.1 send-community extended' - that is correct. Actually, the configuration is correct. But perhaps the issue is that the neighbor is not configured under the IPv4 unicast address-family? That is not required for VPNv4. Hmm. Let me think: The configuration is missing the 'neighbor 10.0.0.1 activate' under the IPv4 unicast address-family? But that is not needed. Actually, the configuration is correct. I need to create a misconfiguration. Let me adjust: The configuration shows 'neighbor 10.0.0.1 send-community extended' but the correct command is 'neighbor 10.0.0.1 send-community extended' - that is fine. Maybe the issue is that the 'neighbor 10.0.0.1 activate' is under the VPNv4 address-family, but the 'send-community' command is missing? No, it's there. Perhaps the problem is that the neighbor is not configured with a route-reflector-client? Not necessarily. I'll change the configuration to have a missing 'send-community extended' to make it wrong.
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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